Telephone services in the past mobile communication systems were provided via a public switched telephone network (PSTN). However, with the recent enhancement of communication technology, wide-band mobile data communication services are enabled, and accordingly, data communication-based Internet telephone services, that is, voice over Internet protocol (VoIP) services, are provided. Accordingly, users can use VoIP communication via an access network providing IP connectivity.
The long term evolution (LTE) system, which is a currently commercialized representative cellular system, also supports the VoIP service. The VoIP service provided through the LTE system may be referred to as “VoLTE.” In the case of the LTE system, a defined codec may be used for the VoIP service, and a bandwidth of at most about 24 Kbps is assigned to each session. When a terminal is positioned in a cell edge region where radio performance is weak, or is not assigned radio resources enough to transmit packets in a weak electric field, the use of a high capacity bandwidth of about 24 Kbps may cause a packet loss. The packet loss may result in degradation of voice quality, and, in the worst case, may cause forced termination of voice communication.